Electric furnace.



i. A. BOECK.

` ELECTRIC FURNAC. APPLICANON FILED NOLQI T911.

1,1 58.972. Patented Nov. 2, 191.5.

UNITED sTATEs PATENT oEEroE.

PERCY A. BOECK, OF WORCESTER, MASSACHUSETTS, ASSIGNOR TO NORTON COMPANY,E WORCESTER, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS.

ELECTRIC FURNACE.

Specification of Letters Patent.

Patented Nov. 2, 1915.

Application filed November 2, 1911. Serial No. 658.092.

I'o all whom 'it may concern.'

Be it known that I, PERCY A. BoECK, a

.citizen of 'the United States, residing at Worcester, in the county oflVorcester and State ofMassachusetts, have invented certain new anduseful Improvements in Electric Furnaces, of which the following is aspecification.

This invention relates to electric resistance furnaces, or analogousconstructions such as electric heaters', rheostats or the like, theobjects of the invention being the provision of an improved constructionof this stood that the principles are equally appli-l cable to theconstruction of other types of electric furnaces or electricf furnaceelements, as for example muffle or Crucible furnaces, heating orresistance elements, and the like. Y

In the drawings, the gureis a central longitudinal section, the centralportion being broken away.

l represents a tube or core of highlyrefractory material of high thermalconductivity, this tube constituting the support for the resistanceelement. As illustrated the tube l is provided with an external helicalgroove 2, in which the resister 3 is coiled. The resister may comprise awire of nickelchromium alloy, platinum, or other suitable material, andis preferably formed, before being wound upon the core or support, intoa continuous coil or helix, which is then wound in the groove 2 in themanner indicated. This construction presents the particularadvantagesthat the length of the resister can be increased to anynecessary' extent, while at the same time the liability of breakage isminimized. The support l should be of a material which in addition tothe necessary refractory character ossesses high thermal conductivity.Suitable materials for the purpose are previously molten alumina grainsbonded by fritting together or by the use of a small proportion of aceramic or basic bond; and silicid of carbon, bonded byre-crystallization or otherwise. l

The core, with the resistance element wound thereon. is filled andcovered with a substantial layer of refractory cement el, and the wholeis covered by a casing 6, which may be of iron. Between the refractorycement 4 and the casing 6 is a filling 5, preferably consisting ofpounded magnesia and constituting an electrical and thermal insulator.As illustrated by way of example, the refractory covering L is formedwith end flanges 4a which support the casing 6 and retain the filling 5.The terminals 3a of the resister 3 extend outwardly through apertures 7in the casing 6 in position for connection to the external circuit.

8 represents a removable cover, which may consist of the same materialas the core 1. It is to be understood that the details of constructionabove described are illustrative only.

The refractory cementA or composition 4 which covers the resistanceelement 3 is composed of grains of previously molten alumina, inconjunction with a relatively small proportion, say'5 to l5 per cent. orsomewhat more, of a suitable bond, as for example a plastic clay, orlime or magnesia. A composition of this character presents veryimportant technical advantages for chemically inactive with respect tothe resister and preserves the wire from corrosion; and by reason of itshigh thermal conductivity, greatly exceeding that of porcelain,lire-clay or the like, it conducts the heat rapidly from the resister,thereby preventing general or localized overheating and consequentinjury. At the same time it aids in the even distribution of heatthroughout the core. Furthermore, by reason of the high specific heat ofthe cement it is adapted to serve as a heat accumulator or equalizer,preventing unduly large fluctuations of the interior temperature whenarticles are introduced `into or removed from the furnace, or when thecovers are removed. It will be understood that a cement of thischaracter may be used in connection with any desired type or core orsupport and resister.

use in this connection: in particular it is .In a furnace or heaterconstructed as herein described, the distribution of the resister issuch as to provide a substantially even temperature-Within the chamber,While at the Same time the coils or turns of the resister are rmly held.The Walls in contact with the resister may be made very thin, and theirthermal conductivity i's such as practically to avoid danger of crackingor checking during rapid changes of temperature.

I claim: p n

1. In an electric furnace, a furnace chamber having Walls'of refractorymaterial, a

resistance element surrounding said Wall,

and a heat-distributing and heat-equalizing envelop comprising4prevlously molten alumina, sald envelop incloslng the resistance elementand Serving to prevent general or local overheating thereof. y

2. In an electric furnace, a furnace charnber having Walls of refractorymaterial, a resistance element surrounding said Wall, aheat-distributing and heat-equalizing envelop comprising previouslymolten alumina, said envelop inclosing the resistance element andserving to prevent general or local overheating thereof, and aheat-insulating pack ing surrounding said envelop. A

In testimony whereof I aliX my signature in presence of two Witnesses.

PERCY A. BOECK.

f Witnesses: i V

ALDUS C. HIGGINS, EARLS: C. MORSE.

